In today's hydro pneumatic spring support systems, two fundamental types have been established, each of which offers particular advantages and disadvantages. On the one hand, these are systems with single acting cylinders or double acting cylinders connected regeneratively in which only the surface of the rod carries the outer force. On the other hand, systems with double acting cylinders are known which are provided with in each case a separate oil circuit and thereby individual springs for each side of the cylinder. While in the case of the single acting systems it is seen as advantageous, that the cost of the configuration is lower than in the case of the double acting cylinders, the latter has the advantage that a pre-load can be established by interaction of the two individual springs formed by the cylinder chambers against each other, that leads to a less over proportional dependance of the spring rate on the immediate load than in the case with single acting cylinders or double acting cylinders connected so as to operate regeneratively. In areas of limited load a nearly proportional behavior can be attained and larger differences between the minimum and maximum spring loads can be operated. The spring rate can also be adjusted by appropriate control of the cylinders.
A relatively rapid adjustment of the spring rate is required for a spring support system independent of external influences such as the contour of the ground or the immediate load adjustable in its damping as well as its spring rate. For this purpose, adjustable dampers had previously been used.
DE 39 02 743 C describes an active wheel or axle support assembly with a hydraulic spring support system of the kind described initially. The chambers of a double acting hydraulic cylinder are connected constantly by adjustable throttle with separate accumulators. Beyond that, the individual chambers separated from each other can be connected by a control or regulating arrangement with the pressure side or the suction side of a hydraulic pump. In the case of a failed operation of the control arrangement actuating the control or regulating valve arrangement or the pump, the control or regulating arrangement takes a position closing the chamber. Accordingly, the mode of operation, in which the chambers of the hydraulic cylinders are connected to the outside only by the accumulator, is used only for an emergency operation.
EP 1 686 045 A describes a self propelled operating machine with a chassis with an operator's station supported upon it by hydraulic cylinders. The piston sides of the hydraulic cylinders are connected permanently with accumulators. In a first switching position a switching arrangement connects the piston chamber of a cylinder with the rod chamber of the particular other cylinder. In another switching position a connection carrying hydraulic fluid is established between the piston chamber of a cylinder and its rod chamber. As a result of the cross connection of the hydraulic cylinders, the first switching position prevents unintended shaking movements of the operators station. The second switching position makes it possible to incline the operator's station in a predetermined region in order, for example, to be able to see an area of the operation that is difficult to observe. The present invention relates to an electronic engine control system which utilizes an exhaust emissions sensor and adaptively maintains a given emissions level.